Liquid crystal drive circuit

ABSTRACT

An electronic timekeeping device includes bipolar integrated circuit implemented logic in combination with a liquid crystal display. The bipolar circuitry is configured to effectively implement logic functions with a supply voltage of 1 volt. Drive circuitry is coupled to the liquid crystal display to effectively impress an a.c. voltage across the liquid crystal cell. Logic of the drive circuitry is effective to provide out of phase voltages across the liquid crystal cell when display is required. When display is not required the voltages across the liquid crystal display cell are in phase such that effectively no potential difference is generated across the liquid crystal material.

tiattea star a w ll Martin Aug. E3, 1974 I LIQUID CRYSTAL DRIVE CIRCUIT Primary Examiner Edith Simmons Jacki-am. lnventor: Robert C. Martin, Dallas, Tex. g rgz l zniold Levine; hdward J. [73] Assignee: Texas Instruments Incorporated,

Dallas, Tex. ABSTRACT i [2*] Filed June 1972 An electronic timekeeping device includes bipolar in PP 263,813 tegrated circuit implemented logic in combination with a liquid crystal display. The bipolar circuitry [52] Us cl 58/50R 307/338 340/336 configured to effectively implement lunctions l5 1] hit Cl u (54b h with a supply voltage of 1 volt. Drive Circuitry is cou- [53] Fie'ld T k pled to the liquid crystal display to effectively impress 307/38. IS 6 1 an ac. voltage across the liquid crystal cell. Logic of the drive circuitry is effective to previde out of phase [56] Reierences Cited voltages across the liquidcrystal cell when display is 7 required. When display is not required the voltages UNITED STATES PATENTS across the liquid crystal display cell are in phase such 3,653,745 4/1972 M ad 350/160 R that effectively no polenfla] difference 15 ggnemted DIeI'ShOCk across the rystal material 3.70l.249 lO/l972 Bcrgey et al. 58/50 R a 3 Claims, 46 Drawing Figures SUPPLY f lliltl'lll'l' ltl-l l llA'l' lt l-LH. a", /6

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1. In a battery operated electronic timekeeping device which includes a frequency source, decode logic, and a liquid crystal display having a back electrode plate and front electrode segments configured in a display format, drive circuitry for impressing an a.c. voltage source across said front electrode segments and said back electrode plate comprising in combination: circuit means coupled to said frequency source for providing an a.c. clock signal; first logic means coupled to said front electrode segments and said back electrode plate for receiving said a.c. clock signal and operably responsive thereto to effect an a.c. voltage at said front electrode segments and said back electrode plate; and second logic means including a plural emitter transistor coupled to each of said front electrode segments for receiving output signals from said decode logic and responsive to the state thereof controlling the a.c. potential at a respective one of said front electrode segments to be either in phase or out of phase with the a.c. potential at said back electrode plate set by said first logic means whereby when said decode logic output signal controls said second logic means to provide out of phase operation the portion of said liquid crystal display including said respective one of said front electrode segments is energized for display and when said decode logic output signal controls said second logic means to provide in phase operation the portion of said liquid crystal display including said respective one of said front electrode segments is not energized.
 2. In a battery operated electronic timekeeping device as set forth in claim 1, wherein said plural emitter transistor is a Schottky transistor.
 3. In a battery operated electronic timekeeping device as set forth in claim 2, wherein said first logic means includes a Schottky transistor having an emitter contact for receiving said a.c. clock signal. 